There is a denial-of-service vulnerability in rp-pppoe versions up to
2.4. rp-pppoe is a user-space PPPoE client for a bunch of UNIXes and
Linux, used by many residential ADSL customers.

If you use the "Clamp MSS" option and someone crafts a TCP packet with
an (illegal) "zero-length" option, rp-pppoe will fall into an endless loop.
Eventually, the PPP daemon should time out and kill the connection.